For the proposed clinical investigation, a cohort of women undergoing the chorionic villus sampling (CVS) procedure at 9-11 weeks gestation will comprise the study group and will be compared with control women equivalent in age, history of abortion, etc. undergoing amniocentesis at 16 weeks. All patients will be scanned ultrasonically for evidence of a viable pregnancy at 8-10 weeks gestation. At their initial visit to the genetics division, women will be recruited for participation in the clinical trial. Women unwilling to accept randomization will become part of the nonrandomized study (CVS) group or the nonrandomized control (amniocentesis) group. Follow-up ultrasound examinations will be conducted at 1 - week post procedure for the CVS group and at 16 and 28 weeks gestation for both groups. Comparisons will be made on a number of maternal outcome variables including post procedure complications. Spontaneous fetal loss will be calculated between 9 and 16 weeks and at 16+ weeks gestation on the combined collaborative sample. The infants born to both groups of women will be examined upon delivery, and will be given physical and developmental examinations at 6 and 12 months of age. Patients' psychological responses to CVS compared to amniocentesis will also be studied at 8, 16, and 28 weeks gestation. The accuracy of prenatal diagnosis using CVS will be evaluated with respect to cytogenetic and biochemical tests, and improvements in the obstetrical procedure will be explored.